Bioloxía do desenvolvemento: Diferenzas entre revisións

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Miguelferig (conversa | contribucións)
Miguelferig (conversa | contribucións)
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[[Ficheiro:Slack Essential Dev Biol Fig 14.12a.jpg|miniatura|esquerda|O sitema Notch-delta na neuroxénese.(Slack Essential Dev Biol Fig 14.12a)]]
 
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A [[Celldiferenciación differentiationcelular]] isé theo processproceso wherebyno differentque functionalse cellorixinan typestipos arisede incélulas development.funcional Fore/ou example,morfoloxicamente neurons,diferentes muscleno fibersdesenvolvemento. andPor hepatocytesexemplo, (liveras cells)[[neurona]]s, are[[fibra wellmuscular|fibras knownmusculares]] typese of[[hepatocito]]s differentiatedson cell.tipos Differentiatedde cellscélulas usuallydiferenciadas. produceAs largecélulas amountsdiferenciadas ofxeralmente aproducen fewgrandes proteinscantidades thatdunhas arepoucas requiredproteínas forque theirso specificnecesarias functionpolas andsúas thisespecíficas givesfncións theme theisto characteristicdálles appearancea thataparencia enablescaracterística themque topermite berecoñecelas recognizedao undermicroscopio theóptico. lightOs microscope.xenes Theque genescodifican encodingestas theseproteínas proteinsson aremoi highly activeactivos. TypicallyA theirsúa estrutura [[chromatincromatina|cromatínica]] structureé ismoi very openaberta, allowingdando accesslibre foracceso thea transcriptionencimas de enzymestranscrición, ande specifica transcriptionfactores factorsde bindtranscrición toespecíficos regulatoryunidos sequencesa insecuencias thereguladoras DNAno inADN orderpara toactivar activatea genesúa expressionexpresión.<ref>Li, B., Carey, M. and Workman, J.L. (2007) The role of chromatin during transcription. Cell 128, 707-719.</ref><ref>Heintzman, N.D., et al. (2007) Distinct and predictive chromatin signatures of transcriptional promoters and enhancers in the human genome. Nat Genet 39, 311-318.</ref> ForPor exampleexemplo, [[NeuroD]] isé aun keyfactor transcriptionde factortranscrición forclave neuronalpara differentiationa diferenciación neuronal, a [[myogeninmioxenina]] foréo musclepara differentiationa diferenciación muscuar, ande o [[HNF4]] forpara a diferenciación hepatocytedos differentiationhepatocitos.
CellA differentiationdifeenciación iscelular usuallyé thexeralmente finalo stageestadio offinal do developmentdesenvolvemento, precededprecedido bypor severalvarios statesestadios ofnos commitmentque whichas arecélulas notquedan visiblycomprometidas differentiateda un dedstino e que non están visiblemente diferenciados. AUn single tissuetecido, formed fromformado a singlepartir typedun of progenitortipo cellde orcélulas stemproxenitoras cellou céllas nais, oftena consistsmiúdo ofconsiste severalen differentiatedvarios celltipos typesde células diferenciadas. ControlO ofcontrol theirda formationsúa involvesformación aimplica processun ofproceso de inhibición lateral inhibition,<ref>Meinhardt, H. and Gierer, A. (2000) Pattern formation by local self-activation and lateral inhibition. Bioessays 22, 753-760.</ref> basedbaseado onnas thepropiedades propertiesdo ofsistema thede sinalización [[Notch-Delta]] signaling system.<ref>Sprinzak, D., et al. (2010) Cis-interactions between Notch and Delta generate mutually exclusive signalling states. Nature 465, 86-90.</ref> ForPor exampleexemplo, inna theplaca neural platedo ofembrión theeste embryosistema thisopera systemxerando operatesunha topoboación generatede acélulas populationprecursoras ofneuronais neuronalnas precursorcales cellsNeuroD in which NeuroDten isunha highlyalta expressedexpresión.
 
=== Rexeneración ===
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[[Regeneration (biology)|Regeneration]] indicates the ability to regrow a missing part.<ref>Carlson, B.M. (2007) Principles of Regenerative Biology. Academic Press, Burlington MA.</ref> This is very prevalent amongst plants, which show continuous growth, and also among colonial animals such as hydroids and ascidians. But most interest by developmental biologists has been shown in the regeneration of parts in free living animals. In particular four models have been the subject of much investigation. Two of these have the ability to regenerate whole bodies: ''[[Hydra (genus)|Hydra]]'', which can regenerate any part of the polyp from a small fragment,<ref>Bosch, T.C.G. (2007) Why polyps regenerate and we don't: Towards a cellular and molecular framework for Hydra regeneration. Developmental Biology 303, 421-433.</ref> and [[planarian]] worms, which can usually regenerate both heads and tails.<ref>Reddien, P.W. and Alvarado, A.S. (2004) Fundamentals of planarian regeneration. Annual Review of Cell and Developmental Biology 20, 725-757.</ref> Both of these examples have continuous cell turnover fed by [[stem cells]] and, at least in planaria, at least some of the stem cells have been shown to be [[cell potency|pluripotent]].<ref>Wagner, D.E., Wang, I.E. and Reddien, P.W. (2011) Clonogenic Neoblasts Are Pluripotent Adult Stem Cells That Underlie Planarian Regeneration. Science 332, 811-816.</ref> The other two models show only distal regeneration of appendages. These are the insect appendages, usually the legs of hemimetabolous insects such as the cricket,<ref>Nakamura, T., et al. (2008). Dissecting insect leg regeneration through RNA interference. Cellular and Molecular Life Sciences 65, 64-72.</ref> and the limbs of [[urodele amphibians]].<ref>Simon, A. and Tanaka, E.M. (2013) Limb regeneration. Wiley Interdisciplinary Reviews-Developmental Biology 2, 291-300.</ref> Considerable information is now available about amphibian limb regeneration and it is known that each cell type regenerates itself, except for connective tissues where there is considerable interconversion between cartilage, dermis and tendons. In terms of the pattern of structures, this is controlled by a re-activation of signals active in the embryo.
There is still debate about the old question of whether regeneration is a "pristine" or an "adaptive" property.<ref>Slack, J.M.W. (2013) Essential Developmental Biology. Chapter 20. Wiley-Blackwell, Oxford.</ref> If the former is the case, with improved knowledge, we might expect to be able to improve regenerative ability in humans. If the latter, then each instance of regeneration is presumed to have arisen by natural selection in circumstances particular to the species, so no general rules would be expected.
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=== Metamorfose ===
Os procesos de desenvolvemento son moievidentes durante o proceso da [[metamorfose]]. Isto ocorre en varios tipos de animais. Son ben coñecidos os exemplos das ras, que normalmente eclosionan en forma de [[cágado]]s e sofren unha metamorfose para converterse en ras adultas, e a de certos insectos que eclosionan comolarvas e despois son remodeladas á forma adulta durante o estadio pupal.